The monofixation syndrome (MFS) is a defective form of binocular vision characterized by preservation of extramacular function with absence of macular fusion. Fusion is defined as the ability to perceive simultaneously similar images projected onto corresponding areas of each retina. The area to fuse images is a binocular phenomenon that occurs in the higher-order parastriate and peristriate areas of the prestriate visuomotor cortex (Brodmann areas 18 and 19, respectively). Patients in this protocol have been examined by Goldmann perimetry and the Lancaster red-green test to map the facultative macular scotoma in the nonfixating eyes in patients with primary MFS, surgically corrected congenital esotropia, and anisometropic amblyopia. The characteristics of the scotomas in each population of patients will be compared. The results of this study will contribute to the understanding of primary MFS by testing the hypothesis that primary MFS is a mild expression of a gene or series of genes that causes congenital esotropia and that these genes exert their variable expression on the binocular neurons of the central macular fusion area.